1. Field of the Invention
The present invention relates to a method and apparatus while drilling a well to aid a choke-operator during well control operations in achieving desired bottom-hole pressure. The invention calculates hydraulic time-delay and pressure attenuation, and includes provisions to account for numerous choke changes and pressure reflections within the hydraulic-delay period using only three inputs, regardless of well depth, pipe and hole geometry, mud properties, temperature, water depth, land, offshore platform or floating (subsea BOP's) drilling rigs.
2. General Background of the Invention
In most geologic basins of the world, drilling for commercial hydrocarbons presents a hazard by virtue of the desired prize itself—flammability of the oil and gas that is contained in the rock strata at high pressures. If these fluids are allowed to surface, they can wreck havoc on the drilling facility that has penetrated the zone. This particular event can be fatal to both rig personnel and neighboring residents.
Fortunately, the spectacular “blow-outs” of Spindletop and other boom areas in the early 1900's have been engineered to “well-control” events that can be “killed” by “well-kill” operations using the constant bottom-hole pressure method. This technique requires maintaining the drill-pipe pressure at given values during the course of the well “kill” which in turn ensures constant bottom-hole pressure at the bottom of the well. This concept is the singular premise of modern well-control to this day, and ensures that adequate pressure is maintained in the wellbore to prevent additional influx of hydrocarbons without fracturing the rock strata.
However, this premise dictates that the pressure on the drill-pipe must be maintained by adjustments on the “back side” or annulus, by suitable restrictions. This is accomplished by adjusting a “choke” mounted on a choke panel that provides back pressure to the circulating system.
It is critical to note that the most difficult aspect of the constant bottom-hole pressure method is maintaining a given pressure on the drill pipe by adjusting the choke on the annulus. This difficulty of maintaining pre-determined pressures is directly related to the hydraulic delay and attenuation of the choke change adjustment as it travels against the flow down the annulus, through the bit and up the drillpipe to the pressure gauge mounted on the choke manifold as per phenomena that is typically studied academically as ‘waterhammer”. This phenomena is not well understood even in this day and age 100 years after Spindletop; the established delay as taught by most well control schools is 2 seconds per 1,000′ of drillpipe length; yet no provisions are made for oil-base vs. water base muds and/or brines. Further, the choke change may not produce the desired change in the drillpipe pressure due to the attenuation of the signal as it travels as much as several miles through the well. Reflections of the pressure wave against the pumps and choke due to choke manipulations are possible and therefore several transit times may be required for the system to stabilize.
The following U.S. Patents are incorporated herein by reference:
TABLEPAT. NO.TITLEISSUE DATE3,827,511Apparatus for Controlling WellAug. 6, 1974Pressure4,253,530Method and System forMar. 3, 1981Circulating A Gas Bubble from aWell5,303,582Pressure-Transient Testing While Apr. 19, 1994Drilling6,575,244System for Controlling theJun. 10, 2003Operating Pressures within aSubterranean Borehole7,261,168Methods and Apparatus for UsingAug. 28, 2007Formation Property Data7,610,251Well Control Systems andOct. 27, 2009Associated Methods2005/0257611Methods and Apparatus forNov. 24, 2005Measuring Formation Properties2007/0107938Multiple Receiver Sub-ArrayMay 17, 2007Apparatus, Systems, and Methods2007/0227774Method for Controlling FluidOct. 4, 2007Pressure in a Dynamic AnnularPressure Control System2007/0246263Pressure Safety System For UseOct. 25, 2007With a Dynamic Annular PressureControl System2008/0097735System for Predicting Changes inApr. 24, 2008a Drilling Event During WellboreDrilling Prior To The Occurrenceof The Event2008/0185143Blowout Preventer Testing SystemAug. 7, 2008and Method2008/0314137Methods and Apparatus forDec. 25, 2008Measuring Formation Properties2009/014330System, Program Products, andAug. 6, 2009Methods for Controlling DrillingFluid ParameterAs above, there have been numerous efforts to improve the well control process; the particular ones listed below are the most pertinent to the present invention:                1. U.S. Pat. No. 3,827,511 discloses a semi-automatic controller that uses a downhole transducer to obtain bottom-hole pressures.        2. U.S. Pat. No. 4,253,530 discloses an automatic controller that utilizes comparators to effect choke changes to maintain desired drill pipe pressures.        3. U.S. Pat. No. 6,575,244 discloses an automated controller that uses lag compensation and/or feedforward control to maintain desired drillpipe pressures. It also describes a system whereby choke changes are initiated by a visual human feedback loop, but are actuated by the control system.        
Fortunately, well control operations are not a common occurrence over the contract period of a particular rig working in a particular area. Therefore, it is difficult to justify and implement a complex control system on drilling rigs in general as described in the above prior art. For example, as control systems become more sophisticated, additional control parameters are introduced that need to be tested and adjusted for certain drilling fluids, influx types, well depths, hole geometry, mud type and properties, temperature profiles, etc. These systems are sometimes used on Managed Pressure Drilling Operations (MPD) but require dedicated personnel to operate and maintain. Since well control operations are not a regular event, it is difficult to impossible to fine-tune an un-manned control system that will react as reliably as a trained and competent human operator. Due to the critical nature and risk of the well control operation, human control will always be desired as crews are trained and certified in well control operations as required by most government agencies around the world.
In contrast to the prior art, the proposed invention provides a means to aid the well control operator to safely circulate out dangerous influxes from the wellbore by employing a device that only requires three inputs, eliminating the need for dedicated personnel to operate and maintain the system.